The Science Journal of the American Association for Respiratory Care

1998 OPEN FORUM Abstracts

IS STERILE WATER NECESSARY IN WICK TYPE HUMIDIFIERS: PART II.

Jim Keenan BS, RRT, Karen Burton RRT, RN, John Salyer BS, RRT. Primary Children's Medical Center, Salt Lake City Utah.

Introduction: This is an ongoing study testing the feasibility of using other than sterile water in wick type humidifiers. The CDC guidelines for infection control recommend the use of..."sterile, distilled or tap water to fill wick humidifiers" [MMWR 1997;46(RR-1):48]. Substituting other water types for expensive sterile water will reduce the costs of mechanical ventilation. Therefore, we set out to investigate whether bacteria inoculated in the chambers of wick type humidifiers could later be found at the patient airway. Methods: Sterile test lungs were constructed with a built in bacterial filter (Nalgene model 130-4045) between the lung and the ventilator circuit (Keenan et al. Respir Care 1997;42:1081). Three Servo 900 C, and three V.I.P. Bird ventilators were operated with a Fisher & Paykel MR 730 wick humidifier, proximal temp. setting 35°C with a chamber control setting of -2°C. Adult circuits were used with the Servo's, neonatal circuits with the Bird's, each with dual heated wires. Each circuit and humidifier were assembled as we do clinically, using no extra sterile precautions to mimic clinical conditions. Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter, and Escherichia coli were prepared in 1.0 mL aliquots of 10^{7} colony forming units per mL. The four solutions were added to sterile water in the humidifiers. The Servo's settings were selected to mimic adult, high flow (50 Lpm) conditions. The Bird's settings were selected to mimic neonatal, continuous low flow (10 Lpm) conditions. The ventilators ran for approximately 24 hours after which the filters were removed aseptically and placed on agar plates for the standard 48 hr. gross growth analysis. All test conditions were repeated four times for a total of 24 runs. Results: One of 24 filters exhibited growth of Pseudomonas aeruginosa. The positive growth was from the Bird neonatal, continuous low flow condition. Conclusion: The single run of our experiment which yielded growth might indicate that bacteria in a wick could contaminate the patient airway. Speculation: Theoretically, organisms of this type cannot be carried in a gas stream that contains only water in the vapor phase. We discussed these theoretical aspects in our previous abstract. It is possible that this single episode of growth could be attributed to the development of microaerosols by the wick type humidifier. It is also possible that organisms were carried in condensate up the inside of the circuit by the gas flows. A third possibility is laboratory contamination, either in our testing lab or in the microbiology lab. These findings cast doubt on the CDC guidelines for using non-sterile water in wick-type humidifiers. However, if our contamination was a result of laboratory error, then the practice of using sterile water may not be warranted. We plan to continue to study this issue.

The 44th International Respiratory Congress Abstracts-On-Disk®, November 7 - 10, 1998, Atlanta, Georgia.

You are here: RCJournal.com » Past OPEN FORUM Abstracts » 1998 Abstracts » IS STERILE WATER NECESSARY IN WICK TYPE HUMIDIFIERS: PART II.